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Home >> Chevrolet >> 2020 >> Express 2500 LS, 6.0L Eng VIN G >> Repair and Diagnosis >> External Pages >> Different car >> Section 15 (Battery, Starting System And Charging System) >> Diagnostic Information and Procedures >> DTC P0621 >> Circuit/System Testing

Circuit/System Testing

WARNING: This page is about a different car, the 2019 GMC Savana 3500, 2019 GMC Savana 2500, 2019 Chevrolet Express 3500, and 2019 Chevrolet Express 2500. However, it is still accessible from the selected car via links, so may be relevant.
  1. Verify a test lamp illuminates between the G13 Generator B+ circuit terminal 1 X2 and ground.
    • If the test lamp does not illuminate and the circuit fuse is good 
    1. Remove the test lamp and disconnect the B+ cable at the G13 Generator.
    2. Test for less than 2 Ω in the B+ circuit end to end.
      • If 2 Ω or greater, repair the open/high resistance in the circuit.
      • If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
    • If the test lamp does not illuminate and the circuit fuse is open 
    1. Remove the test lamp, disconnect the battery negative cable, and disconnect the G13 Generator B+ cable.
    2. Test for infinite resistance between the B+ circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
    • Go to next step: If the test lamp illuminates 
  2. Disconnect the X1 harness connector at the G13 Generator.
  3. Engine Running, test for 3.0 - 5.5 V between the control circuit terminal B and ground.
    • If less than 3.0 V 
    1. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module.
    2. Test for infinite resistance between the control circuit and ground.
      • If less than infinite resistance, repair the short to ground on the circuit.
      • Go to next step: If infinite resistance
    3. Test for less than 2 Ω in the control circuit end to end.
      • If greater the 2 Ω, repair the open/high resistance in the circuit.
      • If less than 2 Ω, replace the K20 Engine Control Module.
    • If greater than 5.5 V 
    1. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module, Ignition ON.
    2. Test for less than 1 V between the control circuit and ground.
      • If greater than 1 V, repair the short to voltage on the circuit.
      • If less than 1 V, replace the K20 Engine Control Module.
    • Go to next step: If between 3.0 - 5.5 V 
  4. Test or replace the G13 Generator.
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